An engine has air supplying and exhausting valves to supply air into and exhaust air from a combustion chamber. These valves are typically a type of side valve system, a top upper valve system or an above valve system, etc. A movable mechanism to open and close these valves, such as a movable valve mechanism of the top upper valve system, is the type with a seesaw type or swing type rocker arm to transmit action of a cam of the camshaft to the valves.
Such a movable valve device is the type equipped on an engine of a multi-cylinder four-cycle type, as shown in FIGS. 7-11. Namely, in FIGS. 7-11, numeral 102 is a multi-cylinder four-cycle engine, 104 is a cylinder head, and 106 is a cylinder head cover. Formed on said cylinder head 104 is a combustion chamber 108 corresponding to each cylinder (not shown) in an axial direction (arrow A in FIG. 9) of the crankshaft (not shown), such as in the lengthwise direction of this cylinder head.
Formed at said cylinder head 104 are an intake port 176 and an exhaust port 178 in the widthwise direction (arrow B direction of FIG. 10) of the cylinder head 104 so as to communicate with an air supply mouth 172 and an exhaust mouth 174 which open into the combustion chamber 108. In the engine 102, the combustion chamber 108 communicates with two air supply mouths 172 and two exhaust mouths 174 and formed in the cylinder head 104 are two air intake and two exhaust ports or passages 176 and 178 respectively for communication with the combustion chamber 108. Respectively provided at the intake and exhaust mouths 172, 174 are air intake and exhaust valves 110, 112. Hence, each cylinder (not shown) is provided with two intake valves 110 and two exhaust valves 112.
Provided in the movable valve chamber 114 (FIG. 10) formed in the cylinder head 104 and cylinder head cover 106 is a movable valve device 116 to open and close the mouths 172 and 174 by opening and closing the valves 110 and 112. A camshaft 118 is positioned eccentric to one side (in widthwise direction) of the cylinder head 104, and extends in the lengthwise direction of the cylinder head 104, and is rotated by a timing belt. This camshaft 118 is rotatably supported at an upper portion of the cylinder head 104 by a camshaft cap 180. This camshaft 118 has thereon, as shown in FIGS. 9-10, two intake cams 122 corresponding to valves 110 associated with one cylinder (not shown) and two exhaust cams 124 corresponding to the exhaust valve 112.
Parallelly provided on an upper portion of the cylinder head 104 are, as shown in FIGS. 9 and 10, a plurality of rocker shaft supports 126 spaced in the lengthwise direction A of the cylinder head. Respectively formed in each of these rocker shaft supports 126 is a hole 128 (FIG. 11) for a holder pipe, which hole is oriented vertically and aligned with the centerline of the combustion chamber. Respectively, inserted into each hole 128 and fixed therein is a holder pipe 132 which forms an ignition plug port 130. Passed from an upper portion through this ignition plug port 130 of each holder pipe 132 is an ignition plug 134 located at a center of the combustion chamber 108 of the cylinder head 104, and fixed on the cylinder head 104.
Provided on an upper part of each rocker shaft support 126 is a rocker shaft cap 140 which pivotably or rotatably supports a rocker shaft 138. This rocker shaft cap 140 is, as shown in FIG. 7, formed with a plug hole 142 oriented vertically therethrough so as to mate to the holder pipe 132, a rocker shaft holding slit 144 at a cap side oriented in a transverse direction at lower face side to hold an upper part of the rocker shaft, and bolt holes 146 through which mounting bolts 180 extend to fix the cap 140 to the support 126.
A plurality of rocker shafts 138 are provided and are located on the same straight line along the lengthwise direction. Each of the rocker shafts 138 is held at opposite ends by neighboring rocker shaft caps 140, as shown in FIG. 9.
Provided swingably on each rocker shaft 138 are a plurality of, such as two, intake rocker arms 148. This intake rocker arm 148 has, as shown in FIG. 8, a pivoting hole 150 at an intermediate part thereof, contact face 152 at one side thereof slidable on an absorbing cam face 122f of the intake cam 122, and an abut member 154 at another side thereof to abut an intake valve stem abut member 110A of the intake valve 110.
Each rocker shaft 138 is located on the same straight line so that a center axial line of the rocker shaft 138 and a center axial line 118C of the camshaft 118 are parallel.
The rocker arm 148 is designed wherein the intake abut member 154 which is a front tip side is formed curved toward the ignition plug 134 side, as shown in FIG. 8, as the ignition plug 134 is located generally at a center part of the combustion chamber 108.
Swingably provided on the upper part of the cylinder head 104 in the movable valve chamber 114, by a headside pivot 188, is a pivot member 186 of a swing type exhaust rocker arm 184, as shown in FIG. 10. In other words, the exhaust rocker arm 184 is provided corresponding to the exhaust cam 124. This rocker arm 184 has the pivot member 186 at one side thereof, a contact face 190 on one face at another side thereof slidable on a cam face 124f of the exhaust cam 124, and an abutting member 192 at another face of this another end side for abutting the stem abutting member 112A of the exhaust valve 112.
Furthermore, there is a prior art four-cycle engine movable valve device, as disclosed in laid open Japanese U.M. Publication No. Sho 63-113704 (1988), which is opened and closed by one camshaft provided with two intake valves and two exhaust valves for one cylinder, wherein an ignition plug inserted in a vertical hole at an upper part of a combustion chamber is provided at a center of the combustion chamber, a camshaft is rotatably pivoted with a shaft on a face of a cylinder head by a bearing cap after it is positioned closer to the exhaust valve, the exhaust rocker arm is swingable, and the rocker shaft is held at opposite ends and pivotably supports the intake rocker arm to the rocker shaft holder attached on the cylinder head so as to surround the vertical hole.
To this end, in the conventional movable valve device of the engine, the ignition plug 134 is, as shown in FIGS. 9 and 11, located at a generally center part of the combustion engine 108, and the intake abutting member 154 of the intake rocker arm 148 is formed curvedly. Furthermore, a central axial line 118C of the camshaft 118 and a central axial line 150C of a support member 150 of the intake rocker arm 148 are provided in parallel. For this reason, a load is provided at point a at the intake abutting member 154 side, and at point b of the axis support member 150 part, and at point c of the absorbing contact face 152 part, as shown in FIG. 8, upon driving of the engine 102. As these load affecting points a, b and c are not positioned on a straight line, there is a drawback in practice in that a fall down is created by loads to each of these points at the intake rocker arm 148 upon opening of the intake valve 110, the intake contact face 152 of the intake rocker arm 148 eccentrically abuts the absorbing cam face 122f of the intake cam 122, and early or rapid wear of the contact face 152 and cam face 122f, burning and abnormal noise, etc., are likely created.
Furthermore, in the conventional intake rocker arm 148, as the abutting member 154 side is curvedly formed and the load affecting point b takes a position on a center axial line 150C of the axis support member 150, a torsional moment is received, and there is a drawback from this shape in that strength/rigidity of the intake rocker arm 148 is lowered.
To overcome this drawback, this invention is characterized in that the movable valve device of the engine comprises a rocker shaft cap to pivot the rocker shaft on an upper part of the engine, said rocker shaft cap being formed with a main body and a plug hole member drilled generally at the center of this main body member, the valves being opened and closed by a camshaft through a rocker arm swingably pivoted on the rocker shaft, wherein a hole engaging member to engage the rocker arm around an outer periphery of said rocker shaft is provided, a center axial line of the axis support at the rocker arm through which said hole engaging member is inserted is slanted with respect to an axial centerline of said camshaft to provide said rocker arm to the engine, and an axial centerline of said hole engaging member is slanted with respect to an axial centerline of said rocker shaft.
In a variation, this invention is characterized in that to solve said drawback, an engine movable valve device comprises one cylinder of the engine having two intake valves and two exhaust valves, an ignition plug is generally at a center part of said combustion chamber, one camshaft opens and closes said intake and exhaust valves, and intake rocker arms and exhaust rocker arms transmit cam operation of this camshaft to said intake and exhaust valves. A cylindrical slanted eccentric spacer cooperates between the rocker arm and rocker shaft so as to slant the pivot axis of the arm pivot with respect to the axial centerline of the cam.
According to the invention, although a contact face of the rocker arm is slanted with respect to the intake cam face of the cam of the camshaft, immediately before functioning of the rocker arm, a face pressure between the contact face and the intake cam face is not likely to cause wear, burning, etc. When the rocker arm begins to operate about the center axial line of the axis support, the contact face of the rocker arm does not eccentrically abut onto the intake cam face of the camshaft, that is the contact face contact is generally evenly applied onto the cam face of the intake cam of the camshaft to prevent early wear, burn and abnormal noise of the contact and cam faces, and to give torsional moment to the rocker arm, and to improve strength/rigidity of the rocker arm.
Now, preferred embodiments will be hereinafter discussed with reference to the accompanying drawings.